Vehicles require energy to move, and when they slow or come to a stop, they dissipate some of that energy into the environment as heat. That heat represents energy that is effectively “lost” or unutilized. Over the years, people have devised mechanical contrivances that attempt to capture some of the vehicle motion energy before it is released as heat. Few of these systems have ever been implemented because of their mechanical complexity, limited energy capture ability, and susceptibility to environmental factors.
One potential response to these issues is to create a vehicle energy harvester that uses moving vehicles to pump a working fluid in the roadway. Using a working fluid can reduce part count and provide a closed system, both of which may improve reliability. Conventional fluid-based approaches have implemented a series of deformable hoses transverse to a roadway or a single large bladder below the roadway. Both methods rely on passing vehicle wheels to compress the hoses and thereby pump fluid within them to drive an electrical generator. However, both approaches are flawed, because they create significant pumping inefficiencies. In the case of transverse hoses, a passing vehicle wheel can compress only a small portion of the fluid-bearing hose and does so very briefly. In the case of a large bladder, a passing wheel will compress only a small portion of the bladder's width, allowing fluid to escape around the wheel without being pumped uniformly towards a generator.
Ideally, a passing wheel would completely seal a compressible hose beneath the roadway and then travel along the length of the hose to expel fluid from one hose end. However, placing one or more hoses along the direction of vehicle travel alone is insufficient. Vehicles travel along a variety of paths within a roadway lane and therefore contact the roadway at variable lateral positions. Consequently, a passing wheel may straddle one or more hoses in a roadway without compressing them, defeating the system. Moreover, a roadway lane cannot be simply packed with longitudinal hoses, because the hoses need separation to flatten as they compress. Therefore the fluid-based vehicle energy harvester, as conceived to date, has the potential to outperform competing energy harvesting approaches, but it faces heretofore unaddressed implementation challenges.